Field of the Invention
The invention concerns a switching configuration for electrical control devices, which is provided in particular for use in control devices in electrical systems of power-driven vehicles.
In modern power-driven vehicles there is a steady increase in the number of electrical components, e.g. electric motors, generators, etc., and electronic components, e.g. actuators, sensors, etc. Components of this kind increase the size and complexity of the electrical system so drastically that the former usual method of connecting individual loads over a cable harness presents greater and greater problems and is associated with an almost unmanageable outlay.
For this reason there has been a change in recent years towards controlling the loads over digital, computerized systems in which a large number of lines, i.e. the cable harness, is replaced by a bus to which the control circuits of the respective loads are connected.
In systems of that kind, all that the load requires in principle in addition to the bus connection is a switchable connection to a power supply. Switching the power supply for the load is usually carried using power semiconductors, such as transistors and thyristors, and presents a considerable challenge in these digital computerized systems.
The higher the current to be switched, the greater are the associated problems in respect to thermal and electrical losses. Modern power-driven vehicles possess a large number of high-current loads, e.g. cooling fan, rear window heating, starter, catalyzer heating, etc.
Furthermore, the switches used for switching the loads should not only perform the usual on/off function but should also possess a degree of artificial intelligence, i.e. be capable of detecting short circuits, interruptions, electrical or thermal overloads, etc., and of carrying out suitable diagnostic functions in order that effective protection against overload is possible. Through communication of that kind of status information to the control system, malfunctions can be detected and appropriate responses can be initiated in order to protect the load, the battery and the switch itself from damage.
The switches currently used are divided into high side and low side switches depending on the mutual configuration of the load and the power supply. The components used for them are generally MOS transistors with power and logic elements integrated in a common substrate.
In the following, intelligent high side MOS switches are brought in for description without any limitation of generality.
The switches for high-current loads must be very low-impedance in order to keep heat development within limits. The use of vertical n-channel MOSFETs is therefore advantageous. In the assembled state the drain connection of these components is generally connected to the chip carrier, also known as leadframe, which is in turn connected with the positive pole of the supply voltage.
One possibility of arranging high side MOS switches of that kind consists of providing a central switch for the power supply and to add to it connected in series respective switches for corresponding high-current and low-current loads.
A central switch of this kind is accompanied by disadvantages insofar as the costs and the series resistance--and therefore the associated power loss--are high. Apart from that, the threshold for short detection is very large for a central switch since it is not possible to differentiate a "soft", i.e. high-impedance, short from the activation of several normal loads.
From Published, Non-Prosecuted German Patent Application DE 24 09 660 A1 an electrical switching, control and/or regulating device for electrical equipment in a power-driven vehicle is known with a housing for pluggable switching elements, in particular relays, which are disposed adjacently and which have output plug contacts. At distribution lines or buslines, mating plug contact components are located which can accept the output plug contacts of the relays. The distribution lines or buslines, which can be realized as a busbar, serve to provide power to the switching contacts of the relays. In addition, every relay is allocated a fuse that is realized as a pluggable switching.